Why did NASA’s rover just find a cannonball on Mars?

Humanity has still yet to find real, concrete, scientifically-supported evidence of extraterrestrial life. We've gotten pretty close, and discovered some chemical markers and other indications that might suggest life once existed somewhere other than Earth, but the hunt is still on for indisputable proof. Well, some Mars watchers now believe they've found it, and it's in the form of a "cannonball."

An oddly-shaped object was captured on camera by the Mars Curiosity rover, laying on the dusty, rocky, red-tinted surface of the planet. It's a ball, and it looks completely out of place. A bluish-grey orb sitting atop of a sea of red. Alien hunters say it's a cannonball, launched during an ancient Martian war. NASA, as you might expect, says they're crazy.